1. Field of the Invention
The present invention relates to methods of and apparatus for drying. In another aspect, the present invention relates to methods of and apparatus for drying wood, to solar collectors, and to wood products. In even another aspect, the present invention relates to methods of and apparatus for solar drying of wood, to curvalinear solar collectors, and to dried wood products.
2. Description of the Related Art
Lumber is a necessary commodity in our society and is obtained from timber only after much processing. Historically, in order to get the timber from the forest to the consumer, the timber industry has had to deal with three separate operations that are sometimes miles apart, the logging operation, the sawing operation and the drying operation.
By its very nature, logging typically occurs in remote, hard to access areas, making it difficult to transport cut lumber away from the logging operation. Since early saw mills were big and cumbersome, not easily moved from place to place, and required large capital investment, a compromise location was selected in order to economically accommodate logging operations from more than one location.
Many years ago, the drying operation only required a large area to air dry, or season, the lumber. Later, kiln dryers were used, but these had to be physically connected to a power source of some type, the availability of the power source governing the placement of the kilns.
Moving the lumber from one operation to another has always been a problem. Early sawmills were situated on water ways. These water way locations were critical to the timber industry as the most practical way to transport newly cut timber to sawing operations, and to power the saws necessary for the sawing operation.
Through the years, with the invention of the gasoline engine, the discovery of electricity, the establishment of railways and many more inventions and discoveries, the timber industry gained the necessary resources to begin refining their operations. Sawmills became more portable and could be located in close proximity to the actual logging operations.
With the advent of wood drying kilns, cut lumber could be more quickly and more suitably dried for consumer use.
Generally in the kiln drying process for lumber, hot air is blown across sawn unseasoned lumber to remove water. The lumber is arranged in stacks with small spacers, commonly referred to as stickers, between each layer so that the hot air is distributed across the faces of the lumber. After passing through the stack of lumber, the hot humid air is either partially vented, or dehumidified, to remove the water vapor before being reheated and recycled though the stacked lumber.
Two common methods of kiln drying are distinguished by the method used for heating and removing of water vapor.
In the first method, standard kiln drying, heat is supplied to the kiln directly, by burning of fossil fuel or indirectly, with steam passing through heat exchangers associated with the kiln. Water vapor is removed from the kiln by venting a portion of the recycled humid air to the atmosphere. Unfortunately, in standard kiln drying water evaporation is energy intensive, and such a kiln requires steam spray for stress relief of lumber at the end of drying which also adds to the energy requirements.
In the second method, dehumidification kiln drying, heat is electrically supplied to the kiln initially by a resistance heater and then with a condenser. Water vapor is condensed and removed from the kiln as water. Dehumidification drying has many drawbacks: (1) the drying process is slow taking twice as long as standard kiln drying; (2) the kiln operates at temperatures below 120.degree. F. because of limitations in the dehumidification equipment; (3) drying rates below 10% moisture are extremely slow and moisture contents of 6% required for furniture-grade lumber cannot normally be achieved; and (4) no capabilities for a humidification period following drying of the lumber required to relieve internal stresses which remain in the lumber are available.
Prior art patents and articles include the following.
"Solar dry kiln for tropical latitudes", William T. Simpson et al., Forest Products Journal, Vol. 34, No. 5, pp. 25-34, discloses a solar dry kiln having an insulated drying compartment attached to a horizontal external solar collector.
U.S. Pat. No. 4,432,147, issued Feb. 21, 1984 to Chen et al., discloses an energy efficient kiln using solar collectors and a refrigeration system that is useful for drying green lumber. Circulating air is heated by solar collectors and then by a condenser of a refrigeration system, passed in contact with lumber, and dehumidified by cooling across the evaporator of the refrigeration system before being reheated to start another cycle.
U.S. Pat. No. 4,831,747, issued May 23, 1989 to Roos et al., discloses a continuous drier for veneer. Temperature sensors and an infrared detector provide the veneer surface temperature to allow for determination of residual moisture of the veneer. The signal from the infrared detector is utilized in the control of blowers in the drying zones near the exit to provide more precise and reliable control in final moisture, allowing for better toleration of variations in dryer load, initial moisture, wood density, and sheet thickness.
U.S. Pat. No. 4,862,599, issued Sep. 5, 1989 to Brunner, discloses a process and apparatus for drying wood. The apparatus includes sensors for measuring wood moisture level and/or the velocity of the air to control air flow to achieve a desired air velocity profile in the plane of admission into a stack of wood to be dried.
U.S. Pat. No. 5,325,604, issued Jul. 5, 1994 to Little, discloses an automatic control system for a wood drying kiln, in which the weight of a representative sample positioned remote from the batch of wood to be dried is monitored to provide its moisture content. This moisture content is utilized to automatically adjust operational parameters within the kiln to provide desired drying conditions for the batch of wood.
To be of commercial value, wood must generally have a stability content and a moisture content of less than 9%, while kiln drying is the general approach utilized to achieve such moisture content, it is an energy expensive process.
Thus, in spite of these advancements in the prior art, there is still the need for improvement in apparatus for and process of drying timber.
Thus, there is another need for an apparatus for and process of drying timber that is energy efficient.
There is even another need in the art for an apparatus for and process of drying timber that is economically efficient.
There is still another need in the art for an apparatus and process of transporting a product while drying it.
There is yet another need in the art for an improved solar panel.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.